Systems and methods for purging a chiller system

ABSTRACT

Embodiments of the present disclosure relate to a heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) system having a purge system configured to purge a vapor compression system of non-condensable gases (NCG). The purge system includes a refrigerant loop configured to circulate a purge refrigerant and a purge heat exchanger configured to place the purge refrigerant in a heat exchange relationship with a mixture of vapor refrigerant and NCG received from the vapor compression system. The purge system further includes a pump configured to draw the mixture from the vapor compression system, increase a pressure of the mixture, and deliver the mixture to the purge heat exchanger. The pump is disposed upstream of the purge heat exchanger, relative to a flow path of the mixture from the vapor compression system to the purge heat exchanger.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of U.S. Provisional Application Ser. No. 62/714,313, entitled “SYSTEMS AND METHODS FOR PURGING A CHILLER SYSTEM,” filed Aug. 3, 2018, which is hereby incorporated by reference in its entirety for all purposes.

BACKGROUND

This application relates generally to purging systems for air conditioning and refrigeration applications.

Chiller systems, or vapor compression systems, utilize a working fluid, typically referred to as a refrigerant that changes phases between vapor, liquid, and combinations thereof in response to exposure to different temperatures and pressures associated with operation of the vapor compression system. In low-pressure chiller systems, some components of the low-pressure chiller systems operate at a lower pressure than the surrounding atmosphere. Due to the pressure differential, non-condensable gases (NCG), such as ambient air, may migrate into these low-pressure components, which may cause inefficiencies in the low-pressure chiller system. Accordingly, the low-pressure chiller system may include a purging system to purge the chiller system of the NCG to enable more effective or efficient operation of the chiller system. However, traditional purge systems used to remove the NCG may be costly, require extensive maintenance, and may experience inefficiencies.

SUMMARY

In an embodiment of the present disclosure, a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system having a purge system configured to purge a vapor compression system of non-condensable gases (NCG). The purge system includes a refrigerant loop configured to circulate a purge refrigerant and a purge heat exchanger configured to place the purge refrigerant in a heat exchange relationship with a mixture of vapor refrigerant and NCG received from the vapor compression system. The purge system further includes a pump configured to draw the mixture from the vapor compression system, increase a pressure of the mixture, and deliver the mixture to the purge heat exchanger. The pump is disposed upstream of the purge heat exchanger, relative to a flow path of the mixture from the vapor compression system to the purge heat exchanger.

In another embodiment of the present disclosure, a purge system for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes a refrigerant circuit configured to circulate a purge refrigerant, a purge heat exchanger disposed along the refrigerant circuit and configured to place the purge refrigerant in a heat exchange relationship with a mixture received from a chiller of the HVAC&R system, wherein the mixture comprises vapor refrigerant and non-condensable gases (NCG), a pump configured to increase a pressure of the mixture upstream of the purge heat exchanger relative to a flow of the mixture from the chiller to the purge heat exchanger, and a controller configured to regulate operation of the purge system such that the pressure of the mixture within the purge heat exchanger is above a threshold value.

In a further embodiment of the present disclosure, a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes a vapor compression system and a purge system configured to purge the vapor compression system of non-condensable gases (NCG). The purge system includes a refrigerant circuit configured to circulate a purge refrigerant, a purge heat exchanger configured to place the purge refrigerant in a heat exchange relationship with a mixture received from the vapor compression system, wherein the mixture comprises vapor refrigerant and the NCG, a first conduit extending from the vapor compression system to the purge heat exchanger and configured to direct the mixture from the vapor compression system to the purge heat exchanger, a pump disposed along the first conduit and configured to increase a pressure of the mixture above an ambient pressure, and a second conduit extending from the purge heat exchanger to the vapor compression system, wherein the second conduit is configured to direct condensed refrigerant from the purge heat exchanger to the vapor compression system.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of an embodiment of a building that may utilize a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system in a commercial setting, in accordance with an aspect of the present disclosure;

FIG. 2 is a perspective view of an embodiment of a chiller of an HVAC&R system, in accordance with an aspect of the present disclosure;

FIG. 3 is a schematic of an embodiment of an HVAC&R system, in accordance with an aspect of the present disclosure;

FIG. 4 is a schematic of an embodiment of an HVAC&R system, in accordance with an aspect of the present disclosure; and

FIG. 5 is a schematic of an embodiment of an HVAC&R system including a purge system, in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure include a purge system for improving efficiency of purging in a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system. For example, in certain low-pressure HVAC&R systems, an evaporator or other component of the HVAC&R system may draw non-condensable gases (NCG), such as ambient air from the atmosphere, into the system due to a pressure differential between the evaporator (or other component) and the atmosphere. The NCG may travel through the HVAC&R system and ultimately collect within the condenser. The NCG may be detrimental to the overall performance of the HVAC&R system, and as such, it is desirable to remove the NCG from the system. To remove the NCG, a purging system may draw a mixture of NCG and vapor refrigerant from the HVAC&R system and condense the vapor refrigerant within a heat exchanger of the purging system to separate the NCG from the refrigerant. To condense the vapor refrigerant, the purging system may greatly reduce the temperature of the mixture. For example, the temperature of the mixture may be reduced to a temperature below approximately 0° F. Moreover, purging systems may utilize a pump to remove the NCG from the heat exchanger after the NCG are separated from the refrigerant. However, the pump operation may cause a reduction of pressure in the heat exchanger, thereby causing some of the previously condensed refrigerant to boil off or evaporate. Some purging systems may cycle the pump on and off with short cycles to reduce the boil off of refrigerant within the heat exchanger. However, this cycling may lead to reliability issues with the pump.

Accordingly, the present embodiments are directed to a purge system that utilizes a pump to increase a pressure of the mixture of NCG and vapor refrigerant before the mixture is delivered to a purge heat exchanger of the purging system. By increasing the pressure of the mixture, the temperature at which the vapor refrigerant condenses within the purge heat exchanger is also increased. Moreover, the pump may increase the pressure of the mixture to a pressure greater than a pressure of the condenser of the HVAC&R system, which itself is greater than atmospheric pressure. Therefore, once the NCG are separated from the refrigerant within the purge heat exchanger, the NCG be at a sufficient pressure to simply be released from the purge heat exchanger to the atmosphere surrounding the HVAC&R system through a valve without the use of a pump. To control and maintain the pressure within the purge heat exchanger, the purge system may utilize one or more expansion devices downstream or upstream of the purge heat exchanger. Additionally, the purge system may maintain the pressure within the purge heat exchanger by utilizing a fixed exit orifice to drain the condensed refrigerant. Accordingly, the purge system may function with decreased cost, improved performance, and increased reliability to remove NCG from the HVAC&R system.

Turning now to the drawings, FIG. 1 is a perspective view of an embodiment of an environment for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system 10 in a building 12 for a typical commercial setting. The HVAC&R system 10 may include a vapor compression system 14 that supplies a chilled liquid, which may be used to cool the building 12. The HVAC&R system 10 may also include a boiler 16 to supply warm liquid to heat the building 12 and an air distribution system which circulates air through the building 12. The air distribution system can also include an air return duct 18, an air supply duct 20, and/or an air handler 22. In some embodiments, the air handler 22 may include a heat exchanger that is connected to the boiler 16 and the vapor compression system 14 by conduits 24. The heat exchanger in the air handler 22 may receive either heated liquid from the boiler 16 or chilled liquid from the vapor compression system 14, depending on the mode of operation of the HVAC&R system 10. The HVAC&R system 10 is shown with a separate air handler on each floor of building 12, but in other embodiments, the HVAC&R system 10 may include air handlers 22 and/or other components that may be shared between or among floors.

FIGS. 2 and 3 are embodiments of the vapor compression system 14 that can be used in the HVAC&R system 10. The vapor compression system 14 may circulate a refrigerant through a circuit starting with a compressor 32. The circuit may also include a condenser 34, an expansion valve(s) or device(s) 36, and a liquid chiller or an evaporator 38. The vapor compression system 14 may further include a control panel 40 (e.g., controller) that has an analog to digital (A/D) converter 42, a microprocessor 44, a non-volatile memory 46, and/or an interface board 48.

Some examples of fluids that may be used as refrigerants in the vapor compression system 14 are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-407, R-134a, hydrofluoro-olefin (HFO), “natural” refrigerants like ammonia (NH₃), R-717, carbon dioxide (CO2), R-744, or hydrocarbon based refrigerants, water vapor, refrigerants with low global warming potential (GWP), or any other suitable refrigerant. In some embodiments, the vapor compression system 14 may be configured to efficiently utilize refrigerants having a normal boiling point of or above about 0 degrees Celsius or 32 degrees Fahrenheit at one atmosphere of pressure, also referred to as low-pressure refrigerants, versus a medium-pressure refrigerant, such as R-134a, or a high pressure refrigerant, such as R-410A. As used herein, “normal boiling point” may refer to a boiling point temperature measured at one atmosphere of pressure.

In some embodiments, the vapor compression system 14 may use one or more of a variable speed drive (VSDs) 52, a motor 50, the compressor 32, the condenser 34, the expansion valve or device 36, and/or the evaporator 38. The motor 50 may drive the compressor 32 and may be powered by a variable speed drive (VSD) 52. The VSD 52 receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor 50. In other embodiments, the motor 50 may be powered directly from an AC or direct current (DC) power source. The motor 50 may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

The compressor 32 compresses a refrigerant vapor and delivers the vapor to the condenser 34 through a discharge passage. In some embodiments, the compressor 32 may be a centrifugal compressor. The refrigerant vapor delivered by the compressor 32 to the condenser 34 may transfer heat to a cooling fluid (e.g., water or air) in the condenser 34. The refrigerant vapor may condense to a refrigerant liquid in the condenser 34 as a result of thermal heat transfer with the cooling fluid. The refrigerant liquid from the condenser 34 may flow through the expansion device 36 to the evaporator 38. In the illustrated embodiment of FIG. 3, the condenser 34 is water cooled and includes a tube bundle 54 connected to a cooling tower 56, which supplies the cooling fluid to the condenser.

The refrigerant liquid delivered to the evaporator 38 may absorb heat from another cooling fluid, which may or may not be the same cooling fluid used in the condenser 34. The refrigerant liquid in the evaporator 38 may undergo a phase change from the refrigerant liquid to a refrigerant vapor. As shown in the illustrated embodiment of FIG. 3, the evaporator 38 may include a tube bundle 58 having a supply line 60S and a return line 60R connected to a cooling load 62. The cooling fluid of the evaporator 38 (e.g., water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable fluid) enters the evaporator 38 via return line 60R and exits the evaporator 38 via supply line 60S. The evaporator 38 may reduce the temperature of the cooling fluid in the tube bundle 58 via thermal heat transfer with the refrigerant. The tube bundle 58 in the evaporator 38 can include a plurality of tubes and/or a plurality of tube bundles. In any case, the refrigerant vapor exits the evaporator 38 and returns to the compressor 32 by a suction line to complete the cycle.

FIG. 4 is a schematic of the vapor compression system 14 with an intermediate circuit 64 incorporated between the condenser 34 and the expansion device 36. The intermediate circuit 64 may have an inlet line 68 that is directly fluidly connected to the condenser 34. In other embodiments, the inlet line 68 may be indirectly fluidly coupled to the condenser 34. As shown in the illustrated embodiment of FIG. 4, the inlet line 68 includes a first expansion device 66 positioned upstream of an intermediate vessel 70. In some embodiments, the intermediate vessel 70 may be a flash tank (e.g., a flash intercooler). In other embodiments, the intermediate vessel 70 may be configured as a heat exchanger or a “surface economizer.” In the illustrated embodiment of FIG. 4, the intermediate vessel 70 is used as a flash tank, and the first expansion device 66 is configured to lower the pressure of (e.g., expand) the refrigerant liquid received from the condenser 34. During the expansion process, a portion of the liquid may vaporize, and thus, the intermediate vessel 70 may be used to separate the vapor from the liquid received from the first expansion device 66. Additionally, the intermediate vessel 70 may provide for further expansion of the refrigerant liquid because of a pressure drop experienced by the refrigerant liquid when entering the intermediate vessel 70 (e.g., due to a rapid increase in volume experienced when entering the intermediate vessel 70). The vapor in the intermediate vessel 70 may be drawn by the compressor 32 through a suction line 74 of the compressor 32. In other embodiments, the vapor in the intermediate vessel may be drawn to an intermediate stage of the compressor 32 (e.g., not the suction stage). The liquid that collects in the intermediate vessel 70 may be at a lower enthalpy than the refrigerant liquid exiting the condenser 34 because of the expansion in the expansion device 66 and/or the intermediate vessel 70. The liquid from intermediate vessel 70 may then flow in line 72 through a second expansion device 126 to the evaporator 38.

In some embodiments, when the vapor compression system 14 is in operation, the evaporator 38 (or other component) may function at a pressure that is lower than the ambient pressure and/or lower than the pressure of an atmosphere surrounding the vapor compression system 14. As such, NCG may be drawn into the evaporator 38 and move through the compressor 32 to gather in the condenser 34. The NCG may cause the vapor compression system 14 to operate inefficiently. Accordingly, the vapor compression system 14 may include features to purge the vapor compression system 14 of the NCG.

For example, as seen in FIG. 5, the vapor compression system 14 includes a purge system 80. The purge system 80 is configured to remove NCG, such as ambient air, from the vapor compression system 14. To this end, the purge system 80 may include a refrigerant loop 82 configured to circulate purge refrigerant through the purge system 80. In certain embodiments, the refrigerant loop 82 may circulate high pressure refrigerant or a refrigerant at a higher pressure than refrigerant utilized in the main refrigerant loop of the vapor compression system 14. Further, the purge system 80 may include a compressor 84 configured to drive the purge refrigerant through the refrigerant loop 82. A condenser 86 is disposed along the refrigerant loop 82 downstream of the compressor 84. The condenser 86 is configured to receive the purge refrigerant from the compressor 84 and place the purge refrigerant in a heat exchange relationship with ambient air to condense the purge refrigerant. Particularly, an air mover 88, such as a blower or a fan, may be configured to force air across the condenser 86 to absorb heat from the purge refrigerant, thereby condensing the purge refrigerant. An expansion device 90 is disposed along the refrigerant loop 82 downstream of the condenser 86. The expansion device 90 is configured to receive the purge refrigerant from the condenser 86 and control (e.g., reduce) a pressure of the purge refrigerant. A purge heat exchanger 92 is disposed along the refrigerant loop 82 downstream of the expansion device 90. The purge heat exchanger 92 is configured to receive the purge refrigerant from the expansion device 90 and place the purge refrigerant in a heat exchange relationship with a mixture of vapor refrigerant and NCG drawn from the vapor compressor system 14 in order to evaporate the purge refrigerant. That is, the purge heat exchanger 92 is configured to circulate the purge refrigerant through coils 94 (e.g., tubes) within the purge heat exchanger 92 such that the purge refrigerant is placed in a heat exchange relationship with the mixture that is contained within a shell 96 of the purge heat exchanger and external to the coils 94.

Particularly, as discussed herein, the purge system 80 is configured to draw the mixture of vapor refrigerant and NCG from the condenser 34 and condense the vapor refrigerant within the purge heat exchanger 92 to separate the mixture into condensed refrigerant and NCG components. The condensed refrigerant is drained to the condenser 34, the evaporator 38, and/or a liquid line of the vapor compression system 14, and the NCG are released into the atmosphere. In this way, the purge system 80 is configured to purge the vapor compression system 14 of NCG.

In some embodiments, the vapor compression system 14 may utilize a controller 100 to control certain aspects of operation of the purge system 80. The controller 100 may be any device employing a processor 102 (which may represent one or more processors), such as an application-specific processor. The controller 100 may also include a memory device 104 for storing instructions executable by the processor 102 to perform the methods and control actions described herein for the purge system 80. The processor 102 may include one or more processing devices, and the memory 104 may include one or more tangible, non-transitory, machine-readable media. By way of example, such machine-readable media can include RAM, ROM, EPROM, EEPROM, CD-ROM, or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by the processor 102 or by any general purpose or special purpose computer or other machine with a processor.

To this end, the controller 100 may be communicatively coupled with one or more components of the purge system 80 through a communication system 106. In some embodiments, the communication system 106 may communicate through a wireless network (e.g., wireless local area networks [WLAN], wireless wide area networks [WWAN], near field communication [NFC]). In some embodiments, the communication system 106 may communicate through a wired network (e.g., local area networks [LAN], wide area networks [WAN]). For example, as shown in FIG. 5, the controller 100 may communicate to a number of elements of the purge system 80, such as expansion devices, air movers, pumps, valves, and other components. In some embodiments, functions of the controller 100 and the control panel 40 (FIGS. 3 and 4) as described herein may be controlled through a single controller. In some embodiments, the single controller may be the control panel 40 or the controller 100.

As discussed above, the NCG may accumulate in the condenser 34 and mix with vapor refrigerant in the condenser 34. A pump 110, such as a reciprocal/diaphragm oil-free vapor pump, may draw the mixture of NCG and vapor refrigerant from the condenser 34 and deliver the mixture to the purge heat exchanger 92 via a first conduit 113 extending from the condenser 34 to the purge heat exchanger 92. For example, the mixture may be at approximately 94° F. and 26 pounds per square inch (psi) prior to entering the pump 110. The pump 110 may raise the pressure of the mixture, such as by approximately 30 psi, so that the mixture is a superheated vapor at approximately 139° F. and 56 psi with a flow rate of approximately 10 lbm/hr (pounds mass per hour) when exiting the pump 110. As the pressure of the mixture increases, the temperature at which the vapor refrigerant of the mixture condenses correspondingly increases. Therefore, the purge heat exchanger 92 may condense the vapor refrigerant at warmer temperatures, thereby resulting in less work done by the purge fluid when compared to a conventional system, and thereby increasing an efficiency of the purge system 80. In certain embodiments, the pump 110 may include two pumps 111 arranged in series along the first conduit 113, such that each of the two pumps 111 divide or share the load of the pump 110. In this manner, wear on the pump 110 may be reduced, which may reduce a frequency of maintenance on the pump 110.

In certain embodiments, the purge system 80 may include a first expansion device 120 (e.g., electronic expansion valve) disposed between the pump 110 and the purge heat exchanger 92 along the first conduit 113. Indeed, the first expansion device 120 may be configured to receive the mixture from the pump 110, adjust a pressure of the mixture, such as by expanding the mixture, and deliver the mixture to the purge heat exchanger 92. By adjusting the pressure of the mixture just before it is supplied to the purge heat exchanger 92, the first expansion device 120 may be configured to precisely control the pressure of the mixture within the purge heat exchanger 92. For example, the controller 100 may be configured to control operation of the pump 110 and/or the first expansion device 120 to maintain the mixture at a constant or substantially constant pressure within the purge heat exchanger 92. By controlling the pressure within the purge heat exchanger 92, the first expansion device 120 may maintain a liquid seal between the vapor compression system 14 and the purge heat exchanger 92. In certain embodiments, the first expansion device 120 may be an electronically controlled expansion device. In such embodiments, the controller 100 may be configured to send one or more signals to the first expansion device 120 to adjust and control the pressure of the mixture as it enters the purge heat exchanger 92. In certain embodiments, the controller 100 may control the first expansion device 120 to set a maximum pressure, such as a pressure threshold or setpoint, at which the mixture enters the purge heat exchanger 92.

However, it should be understood that, in certain embodiments, the purge system 80 may not utilize the first expansion device 120 to adjust or control the pressure of the mixture. In such embodiments, the pump 110 may drive the mixture directly to the purge heat exchanger 92. Operation of the pump 110 may be controlled, adjusted, or modified to control the pressure of the mixture as it enters the purge heat exchanger 92. In certain embodiments, the controller 100 may provide one or more signals to the pump 110 and/or the first expansion device 120 to adjust operation of the pump 110 and/or the first expansion device 120 to achieve a pressure within the shell 96 between approximately 50 psi and 76 psi. To condense the vapor refrigerant of the mixture while at the pressure of between approximately 50 psi and 76 psi, the purge system 80 may control the temperature within the shell 96 of the purge heat exchanger 92 to be between approximately 28° F. and 35° F. or up to approximately 60° F. Particularly, the controller 100 may adjust one or more components (e.g., the compressor 84, the air mover 106, the expansion device 90, or a combination thereof) of the refrigerant loop 82 to adjust the temperature within the shell 96 of the purge heat exchanger 96.

Upon entering the purge heat exchanger 92, the mixture exchanges heat with the purge refrigerant as the purge refrigerant travels through the coils 94, as discussed above. Specifically, the purge refrigerant is configured to absorb heat from the mixture, such that the vapor refrigerant of the mixture condenses into liquid refrigerant and separates from the NCG. Specifically, as the vapor refrigerant condenses into liquid refrigerant, the liquid refrigerant may gather in the bottom of the shell 96 of the purge heat exchanger 92 due to a difference in density between the liquid refrigerant and the NCG. Indeed, the NCG may correspondingly gather above the liquid refrigerant within the shell 96 of the purge heat exchanger 92. As the liquid refrigerant gathers in the bottom of the purge heat exchanger 92, the liquid refrigerant may be drained to the condenser 34 through a fixed exit orifice 124. The fixed exit orifice 124 may provide a liquid seal, such that a pressure within the purge heat exchanger 92 is substantially maintained, or minimally impacted, as the liquid refrigerant drains out of the purge heat exchanger 92. In other words, the fixed exit orifice 124 may block or prevent a backflow of fluid into the purge heat exchanger 92.

In certain embodiments, the purge system 80 may include a second expansion device 126 (e.g., electronic expansion valve) disposed downstream of the fixed exit orifice 124. The second expansion device 126 may increase a pressure drop of the liquid refrigerant as it drains from the fixed exit orifice 124 to the condenser 34. Indeed, the increased pressure drop provided by the second expansion device 126 may provide a liquid seal, in addition to the liquid seal provided by the fixed exit orifice 124, to block or prevent a backflow of fluid from entering into the purge heat exchanger 92. In certain embodiments, the second expansion device 126 may be an electronically controlled expansion device. In such embodiments, the controller 100 may be configured to send one or more signals to the second expansion device 126 to maintain, adjust, or otherwise control the pressure of liquid refrigerant as it passes from the purge heat exchanger 92 to the condenser 34.

As discussed above, the NCG may gather in the purge heat exchanger 92 as the vapor refrigerant is condensed into liquid refrigerant and is separated from the NCG of the mixture. As the NCG builds up in the purge heat exchanger 92, the pressure of the NCG may be higher than the atmospheric pressure. The elevated pressure of the NCG within the purge heat exchanger 92 is enabled due to the pressurization of the mixture by the pump 110 before the mixture is supplied to the purge heat exchanger 92. Accordingly, a solenoid valve 108 may be used to release the NCG to the atmosphere. For example, the solenoid valve 108 may cycle on and off to release the NCG into the atmosphere. In certain embodiments, the controller 100 may send one or more signals to the solenoid valve 108 to control the release of NCG into the atmosphere based on one or more factors, such as a pressure within the shell 96 of the purge heat exchanger 92.

Accordingly, the present disclosure is directed to systems and methods for purging a low-pressure HVAC&R system (e.g., chiller system, vapor compression system) of NCG that may have entered the HVAC&R system during operation. Specifically, a purge system may purge the HVAC&R system of NCG by drawing a mixture of vapor refrigerant and the NCG from a condenser of the HVAC&R system, condensing the vapor refrigerant to separate the mixture into refrigerant and NCG components, and then supplying the condensed refrigerant back to the condenser and venting the NCG to the atmosphere. Prior to condensing the vapor refrigerant, the purge system may increase a pressure of the mixture, such as via a pump disposed along a conduit between the condenser and a purge heat exchanger of the purge system. In this manner, the temperature at which the vapor refrigerant condenses within the purge system is increased, thereby decreasing an amount of heat exchange required by the purge system to condense the refrigerant, and increasing an efficiency of the purge system.

While only certain features and embodiments have been illustrated and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the disclosed techniques, or those unrelated to enabling the claimed embodiments). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation. 

1. A heating, ventilation, air conditioning, and refrigeration (HVAC&R) system, comprising: a purge system configured to purge a vapor compression system of non-condensable gases (NCG), comprising: a refrigerant loop configured to circulate a purge refrigerant; a purge heat exchanger configured to place the purge refrigerant in a heat exchange relationship with a mixture received from the vapor compression system, wherein the mixture comprises vapor refrigerant and the NCG; and a pump configured to draw the mixture from the vapor compression system, increase a pressure of the mixture, and deliver the mixture to the purge heat exchanger, wherein the pump is disposed upstream of the purge heat exchanger, relative to a flow path of the mixture from the vapor compression system to the purge heat exchanger.
 2. The HVAC&R system of claim 1, wherein the purge system comprises an expansion device disposed upstream of the purge heat exchanger, relative to the flow path of the mixture from the vapor compression system to the purge heat exchanger, wherein the expansion device is configured to receive the mixture from the pump and decrease the pressure of the mixture.
 3. The HVAC&R system of claim 1, wherein the purge heat exchanger comprises a fixed exit orifice, wherein the purge system is configured to drain condensed refrigerant through the fixed exit orifice to the vapor compression system, and wherein the fixed exit orifice is configured to provide a liquid seal between the purge heat exchanger and the vapor compression system.
 4. The HVAC&R system of claim 1, wherein the purge system comprises an expansion device disposed downstream of the purge heat exchanger, relative to a flow path of the mixture from the purge heat exchanger to the vapor compression system, wherein the purge system is configured to drain condensed refrigerant through the expansion device, and wherein the expansion device is configured to receive the condensed refrigerant from the purge heat exchanger and decrease a refrigerant pressure of the condensed refrigerant.
 5. The HVAC&R system of claim 1, wherein the purge heat exchanger comprises a valve configured to release the NCG into an atmosphere surrounding the HVAC&R system.
 6. The HVAC&R system of claim 5, wherein the valve comprises a solenoid valve.
 7. The HVAC&R system of claim 5, wherein the pump is configured to induce a pressure differential between the mixture and the atmosphere, such that a first pressure of the NCG within the purge heat exchanger is greater than a second pressure of the atmosphere.
 8. The HVAC&R system of claim 1, wherein the pump comprises a first pump and a second pump arranged in series along the flow path of the mixture from the vapor compression system to the purge heat exchanger.
 9. The HVAC&R system of claim 1, wherein the purge heat exchanger comprises a shell configured to receive the mixture from the pump and a coil disposed within the shell, wherein the purge heat exchanger is configured to direct the purge refrigerant through the coil.
 10. The HVAC&R system of claim 1, wherein the pump is configured to draw the mixture from a condenser of the vapor compression system, and wherein the purge system is configured to direct condensed refrigerant from the purge heat exchanger to the condenser, to an evaporator of the vapor compression system, or to a liquid line of the vapor compression system.
 11. A purge system for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system, comprising: a refrigerant circuit configured to circulate a purge refrigerant; a purge heat exchanger disposed along the refrigerant circuit and configured to place the purge refrigerant in a heat exchange relationship with a mixture received from a chiller of the HVAC&R system, wherein the mixture comprises vapor refrigerant and non-condensable gases (NCG); a pump configured to increase a pressure of the mixture upstream of the purge heat exchanger relative to a flow of the mixture from the chiller to the purge heat exchanger; and a controller configured to regulate operation of the purge system such that the pressure of the mixture within the purge heat exchanger is above a threshold value.
 12. The purge system of claim 11, wherein the controller is configured to regulate operation of the pump such that the pressure of the mixture within the purge heat exchanger is above the threshold value, wherein the threshold value is greater than or equal to an ambient pressure.
 13. The purge system of claim 12, wherein the threshold value is greater than the ambient pressure by a threshold differential value.
 14. The purge system of claim 11, comprising an electronic expansion valve disposed along a conduit extending between the pump and the purge heat exchanger.
 15. The purge system of claim 14, wherein the controller is configured to regulate operation of the pump and the electronic expansion valve such that the pressure of the mixture within the purge heat exchanger is above the threshold value.
 16. The purge system of claim 11, comprising a solenoid valve configured to release the NCG into an atmosphere surrounding the HVAC&R system.
 17. The purge system of claim 11, wherein the pump is configured to draw the mixture from a condenser of the chiller, and wherein the purge system is configured to direct condensed refrigerant from the purge heat exchanger to the condenser, to an evaporator of the chiller, or to a liquid line of the chiller.
 18. A heating, ventilation, air conditioning, and refrigeration (HVAC&R) system, comprising: a vapor compression system; and a purge system configured to purge the vapor compression system of non-condensable gases (NCG), comprising: a refrigerant circuit configured to circulate a purge refrigerant; a purge heat exchanger configured to place the purge refrigerant in a heat exchange relationship with a mixture received from the vapor compression system, wherein the mixture comprises vapor refrigerant and the NCG; a first conduit extending from the vapor compression system to the purge heat exchanger and configured to direct the mixture from the vapor compression system to the purge heat exchanger; a pump disposed along the first conduit and configured to increase a pressure of the mixture above an ambient pressure; and a second conduit extending from the purge heat exchanger to the vapor compression system, wherein the second conduit is configured to direct condensed refrigerant from the purge heat exchanger to the vapor compression system.
 19. The HVAC&R system of claim 18, comprising a solenoid valve coupled to the purge heat exchanger and configured to cycle on and off to release the NCG from the purge heat exchanger.
 20. The HVAC&R system of claim 18, comprising an electronic expansion valve of the purge system, wherein the electronic expansion valve is disposed along the first conduit between the pump and the purge heat exchanger or is disposed along the second conduit between the purge heat exchanger and the vapor compression system. 